Re: [PATCH v2 17/20] nfs: fix ->d_revalidate() UAF on ->d_name accesses

Jeff Layton
2025-01-17T15:12:38Z

On Thu, 2025-01-16 at 05:23 +0000, Al Viro wrote:
> Pass the stable name all the way down to ->rpc_ops->lookup() instances.
>
> Note that passing &dentry->d_name is safe in e.g. nfs_lookup() - it *is*
> stable there, as it is in ->create() et.al.
>
> dget_parent() in nfs_instantiate() should be redundant - it'd better be
> stable there; if it's not, we have more trouble, since ->d_name would
> also be unsafe in such case.
>
> nfs_submount() and nfs4_submount() may or may not require fixes - if
> they ever get moved on server with fhandle preserved, we are in trouble
> there...
>
> UAF window is fairly narrow here and exfiltration requires the ability
> to watch the traffic.
>
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> ---
> fs/nfs/dir.c | 14 ++++++++------
> fs/nfs/namespace.c | 2 +-
> fs/nfs/nfs3proc.c | 5 ++---
> fs/nfs/nfs4proc.c | 20 ++++++++++----------
> fs/nfs/proc.c | 6 +++---
> include/linux/nfs_xdr.h | 2 +-
> 6 files changed, 25 insertions(+), 24 deletions(-)
>
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> index c28983ee75ca..2b04038b0e40 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -1672,7 +1672,7 @@ nfs_lookup_revalidate_delegated(struct inode *dir, struct dentry *dentry,
> return nfs_lookup_revalidate_done(dir, dentry, inode, 1);
> }
>
> -static int nfs_lookup_revalidate_dentry(struct inode *dir,
> +static int nfs_lookup_revalidate_dentry(struct inode *dir, const struct qstr *name,
> struct dentry *dentry,
> struct inode *inode, unsigned int flags)
> {
> @@ -1690,7 +1690,7 @@ static int nfs_lookup_revalidate_dentry(struct inode *dir,
> goto out;
>
> dir_verifier = nfs_save_change_attribute(dir);
> - ret = NFS_PROTO(dir)->lookup(dir, dentry, fhandle, fattr);
> + ret = NFS_PROTO(dir)->lookup(dir, dentry, name, fhandle, fattr);
> if (ret < 0)
> goto out;
>
> @@ -1775,7 +1775,7 @@ nfs_do_lookup_revalidate(struct inode *dir, const struct qstr *name,
> if (NFS_STALE(inode))
> goto out_bad;
>
> - return nfs_lookup_revalidate_dentry(dir, dentry, inode, flags);
> + return nfs_lookup_revalidate_dentry(dir, name, dentry, inode, flags);
> out_valid:
> return nfs_lookup_revalidate_done(dir, dentry, inode, 1);
> out_bad:
> @@ -1970,7 +1970,8 @@ struct dentry *nfs_lookup(struct inode *dir, struct dentry * dentry, unsigned in
>
> dir_verifier = nfs_save_change_attribute(dir);
> trace_nfs_lookup_enter(dir, dentry, flags);
> - error = NFS_PROTO(dir)->lookup(dir, dentry, fhandle, fattr);
> + error = NFS_PROTO(dir)->lookup(dir, dentry, &dentry->d_name,
> + fhandle, fattr);
> if (error == -ENOENT) {
> if (nfs_server_capable(dir, NFS_CAP_CASE_INSENSITIVE))
> dir_verifier = inode_peek_iversion_raw(dir);
> @@ -2246,7 +2247,7 @@ nfs4_lookup_revalidate(struct inode *dir, const struct qstr *name,
> reval_dentry:
> if (flags & LOOKUP_RCU)
> return -ECHILD;
> - return nfs_lookup_revalidate_dentry(dir, dentry, inode, flags);
> + return nfs_lookup_revalidate_dentry(dir, name, dentry, inode, flags);
>
> full_reval:
> return nfs_do_lookup_revalidate(dir, name, dentry, flags);
> @@ -2305,7 +2306,8 @@ nfs_add_or_obtain(struct dentry *dentry, struct nfs_fh *fhandle,
> d_drop(dentry);
>
> if (fhandle->size == 0) {
> - error = NFS_PROTO(dir)->lookup(dir, dentry, fhandle, fattr);
> + error = NFS_PROTO(dir)->lookup(dir, dentry, &dentry->d_name,
> + fhandle, fattr);
> if (error)
> goto out_error;
> }
> diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c
> index 2d53574da605..973aed9cc5fe 100644
> --- a/fs/nfs/namespace.c
> +++ b/fs/nfs/namespace.c
> @@ -308,7 +308,7 @@ int nfs_submount(struct fs_context *fc, struct nfs_server *server)
> int err;
>
> /* Look it up again to get its attributes */
> - err = server->nfs_client->rpc_ops->lookup(d_inode(parent), dentry,
> + err = server->nfs_client->rpc_ops->lookup(d_inode(parent), dentry, &dentry->d_name,
> ctx->mntfh, ctx->clone_data.fattr);
> dput(parent);
> if (err != 0)
> diff --git a/fs/nfs/nfs3proc.c b/fs/nfs/nfs3proc.c
> index 1566163c6d85..ce70768e0201 100644
> --- a/fs/nfs/nfs3proc.c
> +++ b/fs/nfs/nfs3proc.c
> @@ -192,7 +192,7 @@ __nfs3_proc_lookup(struct inode *dir, const char *name, size_t len,
> }
>
> static int
> -nfs3_proc_lookup(struct inode *dir, struct dentry *dentry,
> +nfs3_proc_lookup(struct inode *dir, struct dentry *dentry, const struct qstr *name,
> struct nfs_fh *fhandle, struct nfs_fattr *fattr)
> {
> unsigned short task_flags = 0;
> @@ -202,8 +202,7 @@ nfs3_proc_lookup(struct inode *dir, struct dentry *dentry,
> task_flags |= RPC_TASK_TIMEOUT;
>
> dprintk("NFS call lookup %pd2\n", dentry);
> - return __nfs3_proc_lookup(dir, dentry->d_name.name,
> - dentry->d_name.len, fhandle, fattr,
> + return __nfs3_proc_lookup(dir, name->name, name->len, fhandle, fattr,
> task_flags);
> }
>
> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
> index 405f17e6e0b4..4d85068e820d 100644
> --- a/fs/nfs/nfs4proc.c
> +++ b/fs/nfs/nfs4proc.c
> @@ -4536,15 +4536,15 @@ nfs4_proc_setattr(struct dentry *dentry, struct nfs_fattr *fattr,
> }
>
> static int _nfs4_proc_lookup(struct rpc_clnt *clnt, struct inode *dir,
> - struct dentry *dentry, struct nfs_fh *fhandle,
> - struct nfs_fattr *fattr)
> + struct dentry *dentry, const struct qstr *name,
> + struct nfs_fh *fhandle, struct nfs_fattr *fattr)
> {
> struct nfs_server *server = NFS_SERVER(dir);
> int status;
> struct nfs4_lookup_arg args = {
> .bitmask = server->attr_bitmask,
> .dir_fh = NFS_FH(dir),
> - .name = &dentry->d_name,
> + .name = name,
> };
> struct nfs4_lookup_res res = {
> .server = server,
> @@ -4586,17 +4586,16 @@ static void nfs_fixup_secinfo_attributes(struct nfs_fattr *fattr)
> }
>
> static int nfs4_proc_lookup_common(struct rpc_clnt **clnt, struct inode *dir,
> - struct dentry *dentry, struct nfs_fh *fhandle,
> - struct nfs_fattr *fattr)
> + struct dentry *dentry, const struct qstr *name,
> + struct nfs_fh *fhandle, struct nfs_fattr *fattr)
> {
> struct nfs4_exception exception = {
> .interruptible = true,
> };
> struct rpc_clnt *client = *clnt;
> - const struct qstr *name = &dentry->d_name;
> int err;
> do {
> - err = _nfs4_proc_lookup(client, dir, dentry, fhandle, fattr);
> + err = _nfs4_proc_lookup(client, dir, dentry, name, fhandle, fattr);
> trace_nfs4_lookup(dir, name, err);
> switch (err) {
> case -NFS4ERR_BADNAME:
> @@ -4631,13 +4630,13 @@ static int nfs4_proc_lookup_common(struct rpc_clnt **clnt, struct inode *dir,
> return err;
> }
>
> -static int nfs4_proc_lookup(struct inode *dir, struct dentry *dentry,
> +static int nfs4_proc_lookup(struct inode *dir, struct dentry *dentry, const struct qstr *name,
> struct nfs_fh *fhandle, struct nfs_fattr *fattr)
> {
> int status;
> struct rpc_clnt *client = NFS_CLIENT(dir);
>
> - status = nfs4_proc_lookup_common(&client, dir, dentry, fhandle, fattr);
> + status = nfs4_proc_lookup_common(&client, dir, dentry, name, fhandle, fattr);
> if (client != NFS_CLIENT(dir)) {
> rpc_shutdown_client(client);
> nfs_fixup_secinfo_attributes(fattr);
> @@ -4652,7 +4651,8 @@ nfs4_proc_lookup_mountpoint(struct inode *dir, struct dentry *dentry,
> struct rpc_clnt *client = NFS_CLIENT(dir);
> int status;
>
> - status = nfs4_proc_lookup_common(&client, dir, dentry, fhandle, fattr);
> + status = nfs4_proc_lookup_common(&client, dir, dentry, &dentry->d_name,
> + fhandle, fattr);
> if (status < 0)
> return ERR_PTR(status);
> return (client == NFS_CLIENT(dir)) ? rpc_clone_client(client) : client;
> diff --git a/fs/nfs/proc.c b/fs/nfs/proc.c
> index 6c09cd090c34..77920a2e3cef 100644
> --- a/fs/nfs/proc.c
> +++ b/fs/nfs/proc.c
> @@ -153,13 +153,13 @@ nfs_proc_setattr(struct dentry *dentry, struct nfs_fattr *fattr,
> }
>
> static int
> -nfs_proc_lookup(struct inode *dir, struct dentry *dentry,
> +nfs_proc_lookup(struct inode *dir, struct dentry *dentry, const struct qstr *name,
> struct nfs_fh *fhandle, struct nfs_fattr *fattr)
> {
> struct nfs_diropargs arg = {
> .fh = NFS_FH(dir),
> - .name = dentry->d_name.name,
> - .len = dentry->d_name.len
> + .name = name->name,
> + .len = name->len
> };
> struct nfs_diropok res = {
> .fh = fhandle,
> diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
> index 559273a0f16d..08b62bbf59f0 100644
> --- a/include/linux/nfs_xdr.h
> +++ b/include/linux/nfs_xdr.h
> @@ -1785,7 +1785,7 @@ struct nfs_rpc_ops {
> struct nfs_fattr *, struct inode *);
> int (*setattr) (struct dentry *, struct nfs_fattr *,
> struct iattr *);
> - int (*lookup) (struct inode *, struct dentry *,
> + int (*lookup) (struct inode *, struct dentry *, const struct qstr *,
> struct nfs_fh *, struct nfs_fattr *);
> int (*lookupp) (struct inode *, struct nfs_fh *,
> struct nfs_fattr *);

Reviewed-by: Jeff Layton <jlayton@kernel.org>